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1.
Jiann-Shin Chen D.K. Blanchard 《Biochemical and biophysical research communications》1984,122(1):9-16
Clostridium pasteurianum has two distinct hydrogenases, the bidirectional hydrogenase and the H2-oxidizing (uptake) hydrogenase. The H2-oxidizing hydrogenase has been purified (up to 970-fold) to a specific activity of 17,600 μmol H2 oxidized/min·mg protein (5 mM methylene blue) or 3.5 μmol H2 produced/min·mg protein (1 mM methyl viologen). The uptake hydrogenase has a Mr of 53,000 (one polypeptide chain). Depending upon how protein was measured, the Fe and S= contents (gatom/mol) were 4.7 and 5.2 (by the dye-binding assay) or 7.2 and 8.0 (by the Lowry method). Both reduced and oxidized forms of the enzyme gave electron paramagnetic resonance signals. The activation energy for H2-production and H2-oxidation by the uptake hydrogenase was 59.1 and 31.2 kJ/mol, respectively. In the exponential phase of growth, the ratio of uptake hydrogenase/bidirectional hydrogenase in NH3-grown cells was much lower than that in N2-fixing cells. 相似文献
2.
Ferredoxin or flavodoxin mediates electron flow from H2-hydrogenase to metronidazole[1-(2-hydroxyethyl)-2-methyl-5-nitroimidazole] to cause the reduction of the latter compound. The reduction of metronidazole in solution is irreversible because the reduced compound further decomposes. Since metronidazole loses its absorption peak at 320 nm upon reduction, the rate of reduction can be monitored spectrophotometrically. When a solution of metronidazole at 0.1 to 0.5 mm is supplemented with ferredoxin- andflavodoxin-free hydrogenase and placed under H2, the rate of metronidazole reduction is proportional to the amount of ferredoxin or flavodoxin added. This forms the basis for an assay that can measure 10 to 1000 ng of ferredoxin or 100–1000 ng of flavodoxin/ml of assay mixture. 相似文献
3.
Ewa Gajewska Ewa Niewiadomska Krzysztof Tokarz Mirosława Słaba Maria Skłodowska 《Journal of plant physiology》2013
In this study, we analyzed the toxic effect of Ni during the development of wheat shoots. Typical developmental alterations in carbon metabolism-related parameters reflecting changes associated with the transition of the seedlings from heterotrophic to autotrophic metabolism were observed in the control shoots between the 1st and the 4th days. Adverse effects of 50 and 100 μM Ni became evident starting from the 4th day of growth on the metal-containing media. We found that Ni-induced stimulation of phosphoenolpyruvate carboxylase (PEPC) activity coincided with decrease in the ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) level and with declines in net photosynthetic rate (PN) and stomatal conductance (gs). Application of Ni resulted in increased activities of several dehydrogenases: glucose-6-phosphate dehydrogenase (G6PDH), 6-phosphogluconate dehydrogenase (6PGDH), isocitrate dehydrogenase (NADP-ICDH) and malate dehydrogenase (NADH-MDH). In contrast, the activities of malic enzymes (NADP-ME and NAD-ME) decreased due to Ni stress. Treatment with Ni led to accumulation of glucose and declined concentration of sucrose as well as considerable increases in concentrations of malic and citric acids. Our results indicate that Ni stress redirects the carbon metabolism of developing wheat shoots to provide carbon skeletons for synthesis of amino acids and organic acids as well as to supply reducing power to sustain normal metabolic processes and to support defense mechanisms against oxidative stress. 相似文献
4.
In angiosperms, cyclic electron transport (CET) around photosystem I (PSI) consists of two pathways, depending on PGR5/PGRL1 proteins and the chloroplast NDH complex. In single mutants defective in chloroplast NDH, photosynthetic electron transport is only slightly affected at low light intensity, but in double mutants impaired in both CET pathways photosynthesis and plant growth are severely affected. The question is whether this strong mutant phenotype observed in double mutants can be simply explained by the additive effect of defects in both CET pathways. In this study, we used the weak mutant allele of pgr5-2 for the background of double mutants to avoid possible problems caused by the secondary effects due to the strong mutant phenotype. In two double mutants, crr2-2 pgr5-2 and ndhs-1 pgr5-2, the plant growth was unaffected and linear electron transport was only slightly affected. However, NPQ induction was more severely impaired in the double mutants than in the pgr5-2 single mutant. A similar trend was observed in the size of the proton motive force. Despite the slight reduction in photosystem II parameters, PSI parameters were severely affected in the pgr5-2 single mutant, the phenotype that was further enhanced by adding the NDH defects. Despite the lack of ?pH-dependent regulation at the cytochrome b6f complex (donor-side regulation of PSI), the plastoquinone pool was more reduced in the double mutants than in the pgr5-2 single mutants. This phenotype suggests that both PGR5/PGRL1- and NDH-dependent CET contribute to supply sufficient acceptors from PSI by balancing the ATP/NADPH production ratio. 相似文献
5.
The effect of sodium cholate and other detergents (Triton X-100, sodium dodecyl sulphate, octyl glucoside, myristyltrimethylammonium bromide) on the reduction of plastoquinones (PQ) with a different length of the side-chain by spinach ferredoxin:NADP(+) oxidoreductase (FNR) in the presence of NADPH has been studied. Both NADPH oxidation and oxygen uptake due to plastosemiquinone autoxidation were highly stimulated only in the presence of sodium cholate among the used detergents. Sodium cholate at the concentration of 20 mM was found to be the most effective on both PQ-4 and PQ-9-mediated oxygen uptake. The FNR-dependent reduction of plastoquinones incorporated into sodium cholate micelles was stimulated by spinach ferredoxin but inhibited by Mg(2+) ions. It was concluded that the structure of sodium cholate micelles facilitates contact of plastoquinone molecules with the enzyme and creates favourable conditions for the reaction similar to those found in thylakoid membranes for PQ-9 reduction. The obtained results were discussed in terms of the function of FNR as a ferredoxin:plastoquinone reductase both in cyclic electron transport and chlororespiration. 相似文献
6.
As an energy carrier, hydrogen gas is a promising substitute to carbonaceous fuels owing to its superb conversion efficiency, non-polluting nature, and high energy content. At present, hydrogen is predominately synthesized via chemical reformation of fossil fuels. While various biological methods have been extensively explored, none of them is justified as economically feasible. A sustainable platform for biological production of hydrogen will certainly impact the biofuel market. Among a selection of biological systems, algae and cyanobacteria have garnered major interests as potential cell factories for hydrogen production. In conjunction with photosynthesis, these organisms utilize inexpensive inorganic substrates and solar energy for simultaneous biosynthesis and hydrogen evolution. However, the hydrogen yield associated with these organisms remains far too low to compete with the existing chemical systems. This article reviews recent advances of biochemical, bioprocess, and genetic engineering strategies in circumventing technological limitations to hopefully improve the applicative potential of these photosynthetic hydrogen production systems. 相似文献
7.
Norifumi Muraki Daisuke Seo Tomoo Shiba Takeshi Sakurai 《Journal of molecular biology》2010,401(3):403-2245
Ferredoxin-NAD(P)+ oxidoreductase (FNR) catalyzes the reduction of NAD(P)+ to NAD(P)H with the reduced ferredoxin (Fd) during the final step of the photosynthetic electron transport chain. FNR from the green sulfur bacterium Chlorobaculum tepidum is functionally analogous to plant-type FNR but shares a structural homology to NADPH-dependent thioredoxin reductase (TrxR). Here, we report the crystal structure of C. tepidum FNR to 2.4 Å resolution, which reveals a unique structure-function relationship. C. tepidum FNR consists of two functional domains for binding FAD and NAD(P)H that form a homodimer in which the domains are arranged asymmetrically. One NAD(P)H domain is present as the open form, the other with the equivalent NAD(P)H domain as the relatively closed form. We used site-directed mutagenesis on the hinge region connecting the two domains in order to investigate the importance of the flexible hinge. The asymmetry of the NAD(P)H domain and the comparison with TrxR suggested that the hinge motion might be involved in pyridine nucleotide binding and binding of Fd. Surprisingly, the crystal structure revealed an additional C-terminal sub-domain that tethers one protomer and interacts with the other protomer by π-π stacking of Phe337 and the isoalloxazine ring of FAD. The position of this stacking Phe337 is almost identical with both of the conserved C-terminal Tyr residues of plant-type FNR and the active site dithiol of TrxR, implying a unique structural basis for enzymatic reaction of C. tepidum FNR. 相似文献
8.
PaO体外活力测定需要Fd作还原剂。通过丙酮沉淀法、DEAE柱层析等制备菠菜Fd,并将其应用于HPLC—荧光法研究PaO催化的Pheide α降解反应。结果表明:经DEAE柱层析纯化得到的是氧化型Fd,而未经DEAE柱层析得到的是还原型Fd,还原型Fd可以参与Pheide α降解反应,色谱峰面积可以表示PaO的活力;FCC的HPLC洗脱时间是5.1min,遮光条件下FCC的半衰期是34.66min,PaO在20℃催化Pheide α降解的活力较高。小麦幼苗离体暗诱导衰老过程中PaO活力变化幅度较大,暗处理5d其活力增加24.47倍,“PaO”Chl降解途径在麦类作物叶片衰老过程中普遍存在。 相似文献
9.
The thermodynamics of the formation of binary and ternary complexes between Anabaena PCC 7119 FNR and its substrates, NADP+ and Fd, or Fld, has been studied by ITC. Despite structural dissimilarities, the main difference between Fd and Fld binding to FNR relates to hydrophobicity, reflected in different binding heat capacity and number of water molecules released from the interface. At pH 8, the formation of the binary complexes is both enthalpically and entropically driven, accompanied by the protonation of at least one ionizable group. His299 FNR has been identified as the main responsible for the proton exchange observed. However, at pH 10, where no protonation occurs and intrinsic binding parameters can be obtained, the formation of the binary complexes is entropically driven, with negligible enthalpic contribution. Absence of the FMN cofactor in Fld does not alter significantly the strength of the interaction, but considerably modifies the enthalpic and entropic contributions, suggesting a different binding mode. Ternary complexes show negative cooperativity (6-fold and 11-fold reduction in binding affinity, respectively), and an increase in the enthalpic contribution (more favorable) and a decrease in the entropic contribution (less favorable), with regard to the binary complexes energetics. 相似文献
10.
Eric A. Johnson Miranda M. Russo Dillon B. Nye Jamie L. Schlessman Juliette T.J. Lecomte 《Biochimica et Biophysica Acta (BBA)/General Subjects》2018,1862(12):2660-2673